Items of extremely sensitive nature or very high proprietary value often must be stored securely in a safe or other containment device, with access to the items restricted to selected individuals given a predetermined combination code necessary to enable authorized unlocking thereof. It is essential to ensure against unauthorized unlocking of such safe containers by persons employing conventional safe-cracking techniques or sophisticated equipment for applying electrical or magnetic fields, high mechanical forces, or accelerations intended to manipulate elements of the locking mechanism to thereby open it.
Numerous locking mechanisms are known which employ various combinations of mechanical, electrical and magnetic elements both to ensure against unauthorized operation and to effect cooperative movements among the elements for authorized locking and unlocking operations.
One example of such recently-developed devices is disclosed in U.S. Pat. No. 4,684,945, to Sanderford, Jr., which relates to an electronic lock actuated by a predetermined input through a keyboard outside a safe to a programmable control unit within a housing of the safe. The device has an electric motor for driving a lock-bolt for locking a safe door to the safe housing, and means for displaying codes entered by the user, with a facility for selectively changing the necessary code. The device also has a battery-powered backup circuit maintained in a dormant state to conserve energy until an actuation key is operated. A microprocessor of the unit is programmed to activate a relatively high frequency of power output pulses at the start of movement of a locking bolt by the electric motor, to overcome inertia and any sticking forces on the bolt, and a lower frequency of power pulses to complete the movement of the bolt.
Another example is provided in U.S. Pat. No. 4,674,781, to Reece et al., which discloses an electric door lock actuator and mechanism having manual and electrically driven locking means. This device utilizes a combination of a lost motion coupling and resilient springs for driving a motive means to a neutral position, to thereby isolate an electric motor and gearing from the locking means so that the locking means may be operated manually without back-driving of the electric motor and intermediate gearing.
A major problem with such devices is that they require substantial amounts of electric power to perform their locking and unlocking functions. For securely storing and accessing highly sensitive or valuable items, it is important to avoid depending on the ready availability of sufficient electrical power for driving the locking mechanism. In fact, for many applications, the use of long-life batteries, even to power a small microprocessor, may also be deemed unacceptable.
The stringency of relevant U.S. government specifications is readily appreciated from Federal Specification FF-L2740, dated Oct. 12, 1989, titled "FEDERAL SPECIFICATION: LOCKS, COMBINATION" for the use of all federal agencies. Section 3.4.7, "Combination Redial", for example, requires that once the lock-bolt has been extended to its locked position "it shall not be possible to reopen the lock without completely redialing the locked combination", and defines the locked position as one in which the bolt has been fully extended. Section 3.6.1.3, "Emanation Analysis", requires that the lock shall not emit any sounds or other signals which may be used to surreptitiously open the lock within a specified period. Section 4.5.2.2.4, "Surreptitious Entry", requires that for any lock to be deemed acceptable, attempts shall be made to unlock the lock through manipulation, radiological analysis and emanations analysis, further including the use of computer enhancement techniques for signals or emanations. Even further, Section 6.3.2 defines surreptitious entry as a method of entry such as manipulation or radiological attack which would not be detectable during normal use or during inspection by a qualified person.
In short, for high security storage of sensitive or valuable material, in light of the availability of sophisticated computer-assisted means and methods for unauthorized operation of locking mechanisms, there exists a need for an autonomous locking mechanism that does not require batteries or external sources of power for any purpose, receives and recognizes only specific user-selected combination code information for access, emanates no information useful to persons attempting unauthorized operation, and is made to resist unauthorized operation even when subjected to strong externally imposed electrical, magnetic or mechanical forces, and satisfies other U.S. government specifications. Most important, once the mechanism is put in its locked position it loses all "memory" of the input combination code and requires a totally new and correct provision of the complete combination code to be unlocked again.
The present invention, as more fully disclosed hereinbelow, meets these perceived needs at reasonable cost with a geometrically compact, electrically autonomous, locking mechanism.